纬编针织物弹伸性成因及预估模型

根据纬编针织物结构与特点,分析织物受力后线圈部段转移的基本特征和弹伸性的成因,并就4大纬编基本组织的弹伸性构成进行描述。组织结构复合是产品设计的重要手段,为分析复合结构织物的弹伸性,提出以串联、并联及其复合模型来预测织物弹伸性的方法。以具体织物结构为例,使用串并联模型分析方法分析织物弹伸性,为预测各种纬编结构针织物的弹伸性提供可行方法与依据。

STUDY ON FLOW STRESS OF 7022 ALUMINUM ALLOY SHEET UNDER DIFFERENT TEMPERATURES AND STRAIN RATES

Warm tensile tests for aluminum alloy 7022 sheet are held at different temperatures and strain rates. The range of temperature is 293-773 K and that of the strain rate is 0. 001-0.1 s^-1. The warm tensile properties,relations among temperature,strain rate,and the flow stress are discussed. Constitutive equations under the warm tension are obtained based on revised Hooke law and Grosman equation. It is concluded that flow stress declines with the increase of the temperature and the decrease of the strain rates. The elongation percentage increases with the increase of the temperature and the decrease of strain rate.

缝纫针使用时间对缝制质量的影响

缝纫针是缝纫机上的一个小部件,但它对缝纫质量起着十分重要的作用,并最终影响缝纫外观。从缝纫强力和线迹弹伸性两方面论述了缝纫针的使用时间对缝制质量的影响。

Biaxial tensile properties and elastic constants evaluation of envelope material for airship

This paper presents an experimental study to determine the tensile properties of the envelope fabric Uretek3216L under biaxial cyclic loading.First the biaxial cyclic tests were carefully carried out on the envelope material to obtain the stress-strain data and the corresponding nonlinearity and orthotropy of the material were analyzed. Then for some determination options with different stress ratios the least squares method minimizing the strain terms was used to calculate the elastic constants from the experimental data.Finally the influences of the determination options with different stress ratios and the reciprocal relationship on the elastic constants were discussed.Results show that the orthotropy of the envelope material can be attributed to the unbalanced crimp of their constitutive yarns in warp and weft directions and the elastic constants vary noticeably with the determination options as well as the normalized stress ratios.In real design practice it is more reasonable to use constants determined for specific stress states in particular stress ratios depending on the project＆#39;s needs.Also calculating the structures with two limitative sets of elastic constants instead of using only one set is recommendable in light of the great variety of the constant＆#39;s values.

The crack tip fields of Mode Ⅱ stationary growth crack on bimaterial interface

A mechanical model is established for mode II interfacial crack static growing along an elastic-elastic power law creeping bimaterial interface. For frictional contact of boundary conditions on crack faces, asymptotic solutions of the stresses and strains of near tip-crack are got. It was shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity and there is not the oscillatory singularity the field. Through numerical calculation , it is shown that the frictional coefficient η notably influence the crack-tip field.

Near Crack Line Elastic-Plastic Analysis for an Infinite Plate Loaded by a Pair of Point Shear Forces

The near crack line analysis method was used to investigate a crack loaded by a pair of point shear forces in an infinite plate in an elastic-perfectly plastic solid. The analytical solution was obtained, that is the elastic-plastic fields near crack line and law that the length of the plastic zone along the crack line is varied with external loads. The results are sufficiently precise near the crack line and are not confined by small scale yielding conditions.

Existence and uniqueness theorem for flow and heat transfer of a non-Newtonian fluid over a stretching sheet

Analysis is carried out to study the existence, uniqueness and behavior of exact solutions of the fourth order nonlinear coupled ordinary differential equations arising in the flow and heat transfer of a viscoelastic, electrically conducting fluid past a continuously stretching sheet. The ranges of the parametric values are obtained for which the system has a unique pair of solutions, a double pair of solutions and infinitely many solutions.

Experimental Study on the Mechanical Behavior of Synthetic Fiber Reinforced Concrete

Based on a series of tests and engineering examples, a study on the mechanical behavior of synthetic fiber reinforced concrete is presented. As a result, when fiber content varies from 0.03% to 0.14%, though the synthetic fiber has more influence on low strength-grade concrete than on high strength-grade concrete, it makes little difference to the mechanical behavior of concrete in general. Test results and applications in construction show that the synthetic fiber can enhance the energy-absorbing capacity and deformation performance of concrete effectively.

APPLICATION OF SOME MECHANICAL CONCEPTS TO STRUCTURAL GEOLOGY

This paper discusses some mechanical concepts that have been largely applied to structural geology and tectonics, and addresses the problems and misunderstandings in use of these mechanical terms. The purpose is to stimulate the interests for structural geologists in using the mechanical principles and methods correctly to solve the geodynamic problems.

Study on high speed tension property of B-grade bulletproof steel

In this paper, the high speed tension experiments have been performed on ultra high strength bulletproof steel. The specimen were cut from B-grade bulletproof steel sheet after hard-module quenching with thickness of 2.3 mm. The mechanical properties at strain rates of 0.001 s^-1, 0.01 s^-1, 0.1 s^-1 and 1 s^-1 were carried out on MTSS10, while those at higher strain rates of 200 s^-1, 500 s^-1 and i 000 s^-1 were tested on HTM5020 high speed tension tester and Hopkinson bar. The data from the high speed tension experiments were fitted via Johnson-Cook constitutive equation, and the fracture surface of each specimen was analyzed by scanning electron microscope （SEM）. The results indicate that, the shoot resistance capability of bulletproof steel is closely related to its strength, thickness and flow behaviors under high strain rate. The shoot resistance will be improved in the case of higher strength and better matching between strength and elongation. The Johnson-Cook constitutive equation fitted via experimental data provides fundament to numerical simulation. With the increase of strain rate, the size and depth of dimple trend to decrease and the depth of dimple changes less in steel with lower strength and higher elongation. The SEM analysis of fracture aspect is of benefit for further understanding of deformation and fracture mode under high strain rate.

Tensile behaviors of filaments with misfit of chirality

Slender chiral filaments are ubiquitous in both artificial and biological materials.Due to their chiral microstructures,chiral filaments usually exhibit favorable properties such as superior elasticity and unusual stretch-twist coupling deformation.However,how these chiral microstructures affect the elastic behavior of filaments remains unclear.In this paper,a refined Cosserat rod model with misfit or mismatching of chirality induced by inhomogeneous arrangement of chiral microstructures incorporated is developed.Using the refined rod model,the force-displacement relationships and variation of structural chirality during the tensile processes of two typical helical structures,i.e.,single-strand helix and double-strand helix,are investigated.The results show that the misfit of chirality can lead to a bend-twist deformation with a high coupling degree,which makes the rod much“soft”when stretched.The chiral filaments undergo an unusual twist when stretched,corresponding to an obviously nonlinear variation of structural chirality.The work suggests that the misfit of chirality can be used to tune the elastic behavior of chiral filaments,which is helpful in guiding the design of flexible actuators and soft devices.

Prediction of the internal energy contribution of polydimethylsiloxane during elongation

Rubber elasticity theory is of fundamental importance in polymer science. The traditional theory is athermal, describing rubber deformation behavior as entropy elasticity without an internal energy contribution. It has been found experimentally, however, that the internal energy contribution is not zero. In the present study we have used conformational elasticity theory to calculate the internal energy contribution of polydimethylsiloxane (PDMS) and results obtained are consistent with a number of experimental observations.